Last night I was driving my 94 sub home with a trailer for the first time, when I noticed some things. At 70 mph the truck would surge some? I looked that the temp and it was ok, but the volts were down in the 11.5-12.5 range, is that normal? I have been noticed that when I drive with the AC in the day the same problem. I was thinking I would find out what the deal is before I take off with my blazer on the trailer. This is what I am thinking, 1. alternator is going bad. 2. new Fuel Filter. 3. know it needs a new belt. 4. Friend thinks it my be the battery. What I think I might do is pull the battery from the blazer and put it in the sub and change the belt. It that does not fix, new fuel filter. Last new alternator. If that does not do it I will take to a shop. What do you all think???